The present invention relates to a method for baking wire-like products, and in particular copper wires enamelled with a cladding of insulating plastics resin.
As is known, processes currently used for baking the cladding of electrically conductive wires comprise two stages successively performed in respective first and second regions of an oven, usually of the continuous or tunnel type. During the first stage of the process the solvents which impregnate the layer of synthetic resin cladding the wire are caused to evaporate by heating, while during the second stage of the process the wire is heated to a temperature greater than that of the first stage so as to cause polymerization and cross-linking of the cladding resin, which has insulating properties. During these stages the wire is advanced through the tunnel oven, parallel to the longitudinal axis of this oven, at a predetermined speed. The heating of the oven is usually effected by electrical or gas radiant elements disposed within the oven itself. The evaporated solvent mixes with the air present in the oven which therefore becomes polluted; before discharge, therefore, the stream of air and solvent is subject to a combustion process, conveniently by means of an armored electrical resistance heater unit followed by catalytic plates, which cuts out the major part of the solvent by oxidizing it into non-polluting products such as steam and carbon dioxide.
The known process described above is not entirely free from disadvantages in that, as well as periodically extracting a part of the atmosphere from the furnace and replacing it with fresh air, which is also undertaken for reasons tied to the control of the constancy of the desired temperature in the oven, this involves a rather significant amount of loss of the heat accumulated in the airstream sent to the discharge since the said combustion heater unit is operated at a temperature considerably greater than that of the oven.
Ovens have therefore been made in which a part of the heat in the discharge flow is recovered, in that at least a part of this flow is reintroduced into the oven chamber, for example close to the inlet opening or the outlet opening or both, so as to effect heating of the oven chamber also by convection. This process is not however suitable for the baking of wire-like products of relatively small diameter, less than 0.2 mm, since the direct movement of the air on the wire detrimentally affects the achievement of uniformity in the final characteristics of the wire.